This review summarizes the microbiology and physiology of "Microthrix parvicella" and the methods of its growth control in activated sludge wastewater treatment plants. This filamentous bacterium is of high interest because of its worldwide involvement in severe bulking and foaming at wastewater treatment plants. We present a critical analysis of physiological and kinetic data on "M. parvicella" and discuss its growth and storage abilities in various environments with the aim of understanding the strategies of this organism to successfully compete with other bacteria in activated sludge. Additionally, this review elaborates on research needs for defining reliable control strategies of bulking and foaming based on key features of "M. parvicella".

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Two strains of "Microthrix parvicella" (RN1 and 4B strains) have been physiologically and kinetically characterized by utilizing a new technique particularly suitable for slow growing bacteria. The proposed method is based on the Total Extended Filament Length (TEFL) measure on filaments grown on agar surfaces. This allows us to study more easily and rapidly slow growing bacteria under many different conditions without altering the growth environment during the test. "Microthrix parvicella" appears to have versatile physiological capabilities allowing effective competition against other bacteria in the complex biocenosis of activated sludge. Main peculiarities of this organism are its storage capabilities under an aerobic/anoxic/anaerobic reaction environment, the resistance to long periods of anoxic/anaerobic conditions, the possibility of growing with appreciable kinetics at very low temperatures. In the kinetic characterization low Ks values have been observed; this finding supports the assumption that "Microthrix parvicella" is a "Ks- strategist" with high substrate affinity. Kinetics tests performed in a mixed population of activated sludge bacteria and on pure culture of filaments isolated from the same sludge sample showed that no beneficial effect on the growth rates of "Microthrix parvicella" seems attributable to the presence of activated sludge. This last result confirms the validity of pure culture studies for this microorganism and the reliability of physiological and kinetic data so evaluated in describing real systems.

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Bioremediation as a sustainable alternative to chemical-physical processes is an attractive solution for soil decontamination and renewal of polluted sites. Depending on the site characteristics and target treatment requirements for the decontaminated soil, in situ or ex situ technologies are employed. Ex situ technologies are advantageous when a safe and effective intervention is required (i.e., in the presence of severe contamination of highly hazardous compounds). In this review, conventional and innovative ex situ technologies for soil bioremediation are presented. For each one the principle of operation and recent applications are reported. In addition, strategies to improve their efficiency are explored. Finally, the possibility of making these technologies more competitive by indicating research needs for their future development is highlighted.